Autostereoscopic video device and system

ABSTRACT

The invention relates to a device for display an autostereoscopic image on a video screen (20) having a cylindrical lens array (10) disposed in front of it. The video screen (20) has pixels made up of p color points (RGB) placed horizontally side by side, the number of viewpoints for the autostereoscopic image is different from p×n (where n is a non-zero integer), and the lens array (10) has a pitch equal to the product of the pitch of the color points (R, G, B) multiplied by the number of viewpoints, e.g. four.

FIELD OF THE INVENTION

The present invention relates to a device for displaying anautostereoscopic image on a video screen having a cylindrical lens arrayplaced in front of it.

BACKGROUND OF THE INVENTION

A method and a device for producing autostereoscopic images implementingcylindrical lenses are described in U.S. Pat. No. 5,099,320 filed by theApplicant.

An image produced in this way is generally displayed by means of atelevision having a lens array placed in front of it, with the pitch ofthe array being equal to the product of the pitch of the image points orpixels multiplied by the number of viewpoints for the autostereoscopicimage. In other words, each individual lens of the display lens arraycovers all of the color points of any pixel, and it covers four pixelsfor four viewpoints which are seen in succession and in complementarymanner by an observer with a certain amount of magnification inherent tothe lens array used, the color points being seen as having the samewidth as the lens. The observer therefore does not see the threecomponents of a pixel together.

This gives rise firstly to the image points or pixels being magnifiedand secondly to the array pitch being visible, which pitch is equal tothe width of four pixels, for example, in a display system having fourviewpoints.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a device making itpossible to avoid, at least in part, another of the above-specifieddrawbacks.

To this end, the invention provides a device for displaying anautostereoscopic image on a video screen having a cylindrical lens arraydisposed in front of it, the device being characterized in that thevideo screen has pixels made up of p color points placed horizontallyside by side where p is an integer greater than 1, in that the number ofviewpoints for the autostereoscopic image is different from p×n (where nis a non-zero integer), and in that the lens array has a pitch equal tothe product of the color point (or phosphor) pitch multiplied by thenumber of viewpoints.

For example, for a number of viewpoints equal to 4, the pitch of thelens array corresponds to four color points.

According to the invention, the pitch of the array used is then threetimes smaller than the pitch of the array that would have been used inthe prior art, and in addition, by using lenses at a smaller pitch, itis possible to obtain focal lengths that are smaller and to obtainobserved areas that are smaller, thereby avoiding the observerperceiving the dot structures of color points and pixels on the screen.In addition, for the observer, the size ratio between color points andpixels (1/3) is preserved.

The invention also provides a method of processing an autostereoscopicimage for display via a device as defined above, characterized in thatit comprises a permutation step applied to the color points of pixels sothat an observer sees the three color points of each pixel belonging toeach viewpoint in three successive lenses of the lens array.

Said permutation of the color points can be implemented by permutationof digitized data addresses for the color points while they are beingwritten to or read from an image color point memory.

Said color point address permutation may advantageously be implementedby means of at least one transcoding memory, for at least one line.

In a preferred implementation, the transcoding memory is input addressedby a pixel counter for each line, which counter is reset to zero at thebeginning of each line, and produces, on output, for the image colorpoint memory, permutated addresses corresponding to the permutations ofthe red, green, and blue color points respectively. The image colorpoint memory may also be write addressed by a line counter.

The invention also provides an autostereoscopic video systemcharacterized in that it comprises:

a device for image treatment by permutation of pixel color points; and

a display device as defined above;

and in that said permutation is such that an observer sees the p colorpoints of each pixel belonging to each viewpoint in p successive lensesof the lens array.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention appear moreclearly on reading the following description given with reference to theaccompanying drawings, in which:

FIG. 1a shows a display device of the invention in which there can beseen, in the form of tables, the permutations of the color points forthe various pixels, when there are four viewpoints and the RGB pixelsare in alignment;

FIG. 1b shows the FIG. 1a device but with the pixels disposed in squaresat a pitch of two pixels;

FIG. 2 is a block diagram of an address permutation device having atranscoding memory enabling the method of the invention to be performed;and

FIG. 3 shows tables illustrating, on the left, the permutations in thepixel transcoding memory for the red R, green G, and blue B componentsof an autostereoscopic image, and on the right, the result of writingthe pixels into memory due to the action of the transcoding memory MTP.

DETAILED DESCRIPTION OF THE DRAWINGS

When a video screen is observed through a magnifying glass, it can beseen that the displayed color image is made up of a periodic successionof red (R), green (G), and blue (B) color points, which points shinemore or less brightly, and the resulting color sensation is due to thethree elementary components being subject to a mixing effect in the eyeof the observer.

In the techniques for displaying images in relief without the use ofspectacles, it is necessary to place a converging lens array in front ofthe screen and parallel thereto, at a distance equal to the focal lengthof the vertical axis convex microlenses making up the array. As aresult, the microlenses of the array magnify the points horizontally andthey project the visual information present on the screen to infinity.

When an observer moves parallel to the screen, blue, green, and redpoints are seen in succession in the reverse order to that set up by thestructure of the screen (because of the inversion due to the presence ofthe cylindrical lenses). In the prior art, the array has a pitchcorresponding to an integer multiple of the pixel pitch (in fact it isvery slightly smaller than said value) and, when the observer is at theproper observation distance that corresponds to seeing solid color, i.e.color without moire fringes, depending on the exact position of the headthe observer will see a single color over the entire screen and for eacheye. However, if the observer moves closer or further away, then colormoire patterns appear, particularly when the pitch of the virtual arraythat can be defined as the projection from the eye of the observer ofthe real array onto the structure of the screen is different from thatof the screen structure (three color points per pixel and n pixels perlens, where n is equal to the number of viewpoints for the stereoscopicimage).

The result of this is that the color information completely or partiallydestroys the readability of the image, given that it is impossible tomagnify a pixel without simultaneously magnifying its color components.

The idea on which the invention is based is that the above drawbacks canbe remedied when the video screen has pixels made up of color pointsplaced horizontally side by side.

The invention applies to the case where the number of viewpoints for theautostereoscopic image is different from p or a multiple of p.

According to the invention, a lens array 10 has a pitch equal to that ofan elementary phosphor or color point multiplied by the number ofviewpoints. In the example of FIG. 1, the number of viewpoints is equalto 4. There are thus four horizontally juxtaposed pixels P1 to P4, pixelP1 corresponding in the prior art to the first viewpoint, pixel P2 tothe second viewpoint, pixel P3 to the third viewpoint, and pixel P4 tothe fourth viewpoint. Each of the pixels on the screen 20 has threecomponents, respectively red, green, and blue, written R, G, and B. Thelens array 10 has microlenses L1, L2, L3, etc. at a pitch equal to thewidth occupied horizontally by four juxtaposed color points, i.e. aboutfour-thirds of a pixel. Thus, above-mentioned pixels P1 to P4 correspondto three elementary microlenses L1, L2, and L3. The following pixels P5to P8 corresponding to the adjacent column have, in like manner, threelenses L4, L5, and L6 corresponding thereto.

Depending on its position, the eye of an observer observing the screen20 through the lens array 10 will see either a juxtaposition of the redcomponent R of pixel P1, the green component G of pixel P2, and the bluecomponent B of pixel P3, or a juxtaposition of the green component G ofpixel P1, the blue component B of pixel P2, and the red component R ofpixel P4, or a juxtaposition of the blue component B of pixel P1, thered component R of pixel P3, and the green component G of pixel P4, orfinally a juxtaposition of the red component R of pixel P2, the greencomponent G of pixel P3, and the blue component B of pixel P4. In otherwords, each eye of the observer is likely to mix visually the red, greenand blue components of different pixels in the image.

Naturally, the example given above with lenses L1, L2, and L3 is equallyapplicable to lenses L4 to L6, with pixels P5 to P8, and so on.

In this way, the observer always perceives a succession of microlensesof complementary colors distributed at a pitch over the entire screen,with the apparent pixel pitch always remaining equal to four pixels asbefore, in the prior art, so stereoscopic vision is not changed, but nowthree microlenses are required to achieve the effect, instead of asingle microlenses that is three times larger (an array 30 of lenses Lshown in dashed lines in FIG. 1).

As shown above, to conserve image information, it is necessary to changethe position of the red, green, and blue information of images in reliefpresented in this manner since a given pixel now comprises informationrelating to three different viewpoints. This is achieved by permutationof the color components for each viewpoint relative to one another inapplication of the following rule:

for viewpoint No. 1 which, in the prior art used to be containedentirely in the first pixel P1, the red component R remains in place (0)while the green component G is shifted one pixel to the right (+1) andthe blue component B is shifted two pixels to the right (+2) (tripletTR1);

for viewpoint No. 2 which, in the prior art used to be containedentirely in the second pixel P2, the green component G remains isshifted one pixel to the left (-1) and the blue component B stays inplace (0) and the red component R is shifted two pixels to the right(+2) (triplet TR2);

for viewpoint No. 3 which, in the prior art used to be containedentirely in the third pixel P3, the blue component B is shifted twopixels to the left (-2), the red component R stays in place (0) and thegreen component G is shifted one pixel to the right (+1) (triplet TR3);and

for viewpoint No. 4 which, in the prior art used to be containedentirely in the fourth pixel P4, the triplet TR4 is obtained by shiftingthe red component R two pixels to the left (-2), the green component Gone pixel to the left (-1), and the blue component B stays in place (0).

This is represented in the tables in boxes in FIG. 1a in which thenumbers NTR of the pixels on the screen correspond to theabove-specified triplets TR1, TR2, TR3, and TR4 and in which thedisplacement DPC to be performed on the color components of the pixelsto be displayed is represented by the above increments, whereas theposition PPC of the pixels coming from the camera is given by PX4 fortriplet TR1, PX3 for triplet TR2, PX2 for triplet TR3, and PX1 fortriplet TR4. This corresponds to inversion of the elementary images (bygroups of pixels equal in number to the number of viewpoints, in thiscase four), which inversion must be performed on playback from a rawimage obtained by a cylindrical lens camera in order to obtain anorthostereoscopic image. Such inversion is described in above-mentionedU.S. Pat. No. 5,099,320.

FIG. 1b corresponds to liquid crystal screens (1024×1024) from GeneralElectric or Thomson CSF. The pixels are distributed over a square, eachsquare having a red pixel R and a blue pixel B on one diagonal and twohalf-intensity green pixels G on the other diagonal. The processing tobe performed is similar to the above, but at a pitch of two pixelsinstead of three, i.e. as though the image was a two-color image. Inthis example, a number of viewpoints must be odd (in this case three)and each lens L'1, L'2, L'3, etc. must be of a width covering threepixels. The pixel permutation corresponding to this case is shown inFIG. 1b.

In FIG. 2, an analog video signal VID is applied to the input of ananalog-to-digital converter ADC which in conventional manner generates asynchronization signal SY and digital signals which are applied to a 3×8bit bus for the red component NR, the green component NG, and the bluecomponent NB. The synchronization signal SY is applied to the input of aphase locking and synchronization circuit BVP/SYN which produces asoutputs simultaneously a pixel clock signal 2HLP at twice the pixelrate, a line synchronization signal SYNL, a field parity signal PRT, afield synchronization signal SYNT, and a synchronization signal SYNCTTL.

The pixel clock signal 2HLP is applied to the input of a divide-by-twocircuit D1 which is reset to zero at the beginning of each line by theline synchronization signal SYNL. The pixel clock signal HLP produced atthe output of D1 is applied to the input both of a pixel precounter PCPand to one of the inputs of an AND gate E1 whose other input receivesthe output from the pixel precounter PCP. The pixel precounter PCP islikewise reset to zero at the beginning of each line by the linesynchronization signal SYNL, which also resets to zero the working pixelcounter CPI whose input is constituted by the output of the AND gate E1.The output of the working pixel counter CPI is a 10-bit bus which feedsthe address inputs of pixel memories, in particular a red pixel memoryMPR1, a green pixel memory MPG1, a blue pixel memory MPB1, for storing afirst image, and a second red pixel memory MPR2, a second green pixelmemory MPG2, and a second blue pixel memory MPB2 for storing the secondimage. The output of the circuit CPI is connected to the address inputsof these memories both directly for reading purposes and indirectly viatranscoding memories MTPR for the red color points, MTPG for the greencolor points, and MTPB for the blue color points for writing purposes.It will be observed that it is also possible to perform transcoding onreading. In which case, the transcoding memories MTPR, MTPG, and MTPBshould be disposed between the output of the circuit CPI and the readaddressing of the memories MPR1, MPG1, MPB1, MPR2, MPG2, and MPB2. Theline synchronization signal is also applied to the count input of a lineprecounter PCL and to one of the inputs of an AND gate E2 whose otherinput is connected to the output of the counter PCL. The output of theAND gate E2 is applied to the count input H of a working line counterCLU. The circuits PCL and CLU are reset to zero by the fieldsynchronization signal SYNT. The output from the working line countercircuit CLU is applied via a 10-bit to the write and read address inputsof the memories MPR1, MPG1, MPB1, MPR2, MPG2, and MPB2. For writing, the8-bit buses carrying the digital color signals NR, NG, and NB feed thedata inputs of the respective memories MPR1 and MPR2 for red (NR), MPG1,and MPG2 and green (NG), and MPB1 and MPB2 for blue (NB). The data ofthe above-specified memories is applied on reading to the data inputs ofa digital-to-analog converter ADC synchronized by the signal SYNC TTL.The memories MRP1, MPG1, MPB1, MPR2, MPG2, and MPB2 are separated intotwo portions, e.g. for 1024 lines, the first 512 lines correspond to thefirst field of an image and the last 512 lines correspond to the secondfield. While an image is being written into the memories MPR1, MPG1, andMPB1, an image is being read from the memories MPR2, MPG2, and MPB2, andvice versa. As a result, the operations of writing and reading areseparated. Switching between reading and writing is performed inresponse to a field parity signal PRT as divided by two by divider D2.

The left portion of FIG. 3 shows the permutation table recorded in thepixel transcoding memories MTP (R, G, B). The first input address oraddress 0 corresponds on writing to address 3, i.e. triplet No. 4 TR4.As shown in FIG. 1, the offset is -2 for red, -1 for green, and 0 forblue. For the second address, 1, which corresponds in writing to tripletTR3, the respective offsets are 0 for red, +1 for green, and -2 forblue. For the third address, 2, which corresponds in writing to thetriplet TR2, the offsets are +2, -1, and 0, and for the fourth address,No. 3, which corresponds in writing to triplet TR1 of address 0, theoffsets are 0, +1, and +2. Similarly, the following input addresses 4,5, 6, and 7 correspond in writing to triplets TR8 in address 7, TR7 inaddress 6, TR6 in address 5, and TR5 in address 4. The conversion tableis the same as for the respective write address 3, 2, 1, and 0.

When writing in the pixel memories MTR, for a pixel number NP=1, andwrite address data ADR=0, the write address is equal to 4 for blue (P4),to 3 for green (P3), and to 2 for blue (P2). For the following triplet(TR3), the address is equal to 3 for red (P3), to 4 for green (P4), andto 1 for blue (P1). For the third triplet (TR2), corresponding to pixelPX3, the red component is to be written in the fourth position (P4), thegreen component in the first position (P1), and the blue component inthe second position (P2). Finally, for the fourth pixel PX4corresponding to triplet TR1, red goes for the first position (P1),green to the second position (P2), and blue to the third position (P3).For the following pixels with pixel numbers NP 5 to 8, the table can bededuced from the above table by adding the number 4, and so on.

It may be observed that the transcoding system described above is one inwhich the image is converted into digital form and then back into analogform. It may be observed that such transcoding can be done in analogform, in particular by integrating it in a CCD sensor in which atranscoding circuit is hard-wired between the pixel outputs of the imagepoint columns and the inputs to a shift register so as to achieve thedesired color permutation.

What is claimed:
 1. A device for displaying an autostereoscopic image ona video screen having a cylindrical lens array disposed in front of it,and comprising cylindrical lenses each having an axis parallel to adirection, and the video screen having pixels made up of p color pointsplaced side by side perpendicularly to said direction, where p is aninteger greater than 1, the number of viewpoints for theautostereoscopic image being different from p×n where n is a non-zerointeger, and wherein the lens array has a pitch equal to the product ofthe color point pitch multiplied by the number of viewpoints.
 2. Adevice according to claim 1, characterized in that p is equal to 3 andin that the number of viewpoints is equal to four, the pitch of the lensarray corresponding to four color points.
 3. An autostereoscopic videosystem, which comprises:a device for processing an image by permutationof pixel color points; and a display device according to claim 1andwherein said permutation is such that an observer sees the p colorpoints of each pixel belonging to each viewpoint in D successive lensesof the lens array.
 4. A method of processing an autostereoscopic imagefor the purpose of being displayed by a device having a video screen andan array of cylindrical lenses each having an axis parallel to adirection and disposed in front of the video screen, the video screenhaving pixels made up of p color points placed side by sideperpendicularly to said direction, the autostereoscopic image being madeup of a number of viewpoints which number is different from p×n, n beinga non-zero integer, the lens arras having a pitch equal to the productof the color point pitch multiplied by the number of viewpoints, themethod including a step of pixel color point permutation such that anobserver sees the p color points of each pixel belonging to eachviewpoint in p successive lenses of the lens array.
 5. A methodaccording to claim 4, wherein said color point permutation is performedby permutation of addresses for digitized data of the color points whilethey are being recorded in an image color point memory.
 6. A methodaccording to claim 5, wherein said permutation of color point addressesis performed by at least one transcoding memory.
 7. A method accordingto claim 6, wherein the transcoding memory is input addressed by a pixelcounter for each line, which counter is reset to zero at the beginningof each line, and produces, on output, for the image color point memory,permutated addresses corresponding to the permutations of the red, greenand blue color points respectively.
 8. A method according to claim 7,wherein the image color point memory is also write addressed by a linecounter.
 9. A method according to claim 5, wherein said permutation ofcolor point addresses is performed by at least one transcoding memory.10. A method according to claim 9, wherein the transcoding memory isinput addressed by a pixel counter for each line, which counter is resetto zero at the beginning of each line and produces, on output, for theimage color point memory, permutated addresses corresponding to thepermutation of the red, green and blue color points, respectively.
 11. Amethod according to claim 4, wherein said color point permutation isperformed by permutation of digitized data addresses for color pointswhile they are being read from an image color point memory.